Unable to start the beaglebone black

When bone is connected with the pc through the mini usb the power ed blinks and then it turns off but when i put an external power supply the bone is working. Is my board’s mini usb is Dead??

Most likely your PC port is unable to supply enough current to the board and it shuts down.

Gerald.

i have also used it with the externally powered usb hub but still the power led turns on and the 4 leds blink and then everything turns off. previously i use to connect it with the HDMI but now i am unable to use it over USB

Added information always helps. You could have damaged the USB power input, or the power could exceed 500 mA on your board even on a powered USB HUB.

Gerald
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When i connect the bone with the external power connected still i am not able to connect so i guess the USB power input have been damaged.

Ah, some more information. Sounds like it.

Gerald